What are the reasons for downfall of Islamic societies?

SHAFAQNA – Imam Ali said: Know that, after Hegira, you have become like dessert Arabs, and after untity and brotherhood, have turned into different factions, you only know a name from Islam, and you only recognize a sign from the belief. You only chant slogans, yes to fire, disgrace never! It seems you want to overturn Islam, and tear its curtain of respect? And break the covenant which God placed on the earth for protecting the dignity of Muslims, and a factor of peace and security of the people [1].